Every time you see a lady beetle, you should tuck the bug in your wallet as they are prosperity-bringing lucky charms, according to folklore in many countries.

There’s a grain of truth in the old stories. Every lady beetle in a cotton field in the North China Plain provides an economic benefit to farmers of at least 0.05 yuan (US$ 0.01).

This may not sound like much but doubling the current lady beetle density in two-thirds of Chinese cotton fields could bring farmers around US$300 million per year.

Lady beetles eat aphids that destroy cotton plants. Chinese farmers generally kill aphids using chemical insecticides. Long seen as the easiest and most affordable pest control method, insecticides are used on a mass scale worldwide.

Natural solutions

But chemical insecticide use suppresses the services nature offers for free. For aphids, the pretty and popular red and black beetles are vicious predators. Unleashed onto a field, it is estimated that one lady beetle can kill 50 aphids per day, or some 5,000 in its lifetime.

Chinese fields host about 13,500 lady beetles per hectare. Doubling the average density of our spotted friends could potentially increase farmers’ income by 644 yuan (US$93.67) per hectare. Spread across two-thirds of cotton acreage in China, and that’s nearly two billion yuan (US$290.8 million) pumped into the economy per year.

Wide benefits

Proliferation of lady beetles could address more than the aphid problem. There are health and environmental benefits to farmers and society if chemical insecticide use is reduced.

Excessive use of insecticides by Chinese farmers carries environmental costs as the chemicals infiltrate food, water and ecosystems.

Excessive pesticide use also disrupts natural pest suppression systems by killing not only pests but other important organisms, such as lady beetles, feeding into a vicious cycle of increasingly frequent pest outbreaks due to pesticide resistance.

Pesticides can also undermine the profitability of farms. Insecticide use is expensive and can put farmers on a “pesticide treadmill” where they forgo other solutions. China’s farmers could bolster their long-term bottom line by purchasing less insecticide.

Escalating gains

Our research shows that the less pesticides farmers use, the more lady beetles can expand their aphid-killing services.

If we cut current, excessive insecticide use of 22.35 kilograms per hectare to one quarter of this amount, the marginal value of the ladybirds would rise from more than two and a half times, from 48 yuan (US$6.98) to 118 yuan (US$17.6) per hectare.

Once the biological control services – in this case lady beetles services in cotton fields – begin to flourish, farmers may reduce insecticide use even further, though additional incentives may be needed. However, the value of lady beetles and other natural predators could rise, creating the virtuous cycle that sustainable agriculture urgently needs.

The findings provide a strong economic, health and environmental case for policies that move away from chemicals and provide more support to farmers to reduce pest risks.

But too often, farmers and policymakers lack this knowledge. How can we change this? First, we need to quantify and disseminate the hidden values of biological pest controls. Communicating these should be prioritised, for example, through the agricultural extension service, which can also share information on health risks and adverse environmental effects of agrochemicals.

Five facts about ladybirds

Ladybugs aren’t in fact bugs, but beetles

The lady in the name lady beetle refers to the Virgin Mary. In the Middle Ages, farmers whose crops were plagued by the beetles would pray to the Blessed Lady for deliverance.

Lady beetles are cannibals

The properties of lady beetles wings are currently being researched for robotics, mechanics and aerospace engineering (for their storage qualities and strength)

Lady beetles release noxious compounds from their knees when threatened

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